Armbruster B, Drexlin G, Eitel K, Jannakos T, Kleinfeller J, Maschuw R, Oehler C, Plischke P, Reichenbacher J, Steidl M, Zeitnitz B, Gemmeke H, Kleifges M, Eichner C, Ruf C, Bodmann BA, Finckh E, Hössl J, Jünger P, Kretschmer W, Wolf J, Booth NE, Blair IM, Edgington JA. Improved limits on nu(e) emission from mu+ decay.
Phys Rev Lett 2003;
90:181804. [PMID:
12786000 DOI:
10.1103/physrevlett.90.181804]
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Abstract
We investigated mu(+) decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for nu(e) via the detection reaction p(nu(e),e(+))n. No nu(e) signal from LF violating mu(+) decays was identified. We extract upper limits of the branching ratio (BR) for the LF violating decay mu(+)-->e(+)+nu(e)+nu(-) compared to the standard model (SM) mu(+)-->e(+)+nu(e)+nu(mu) decay: BR<0.9(1.7) x 10(-3) (90% C.L.) depending on the spectral distribution of nu(e) characterized by the Michel parameter rho=0.75(0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which nu(e) emission from mu(+) decay is allowed with considerable strength. The decay mu(+)-->e(+)+nu(e)+nu(mu) often proposed as a potential source for the nu(e) signal observed in the LSND experiment can be excluded.
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